There are many occasions where it is necessary to process and transmit color computer video signals over communications links. In one such instance, when analog VGA video and keyboard signals are routed between one of a plurality of computers and a single monitor and keyboard by switching equipment, such as the COMMANDER module, manufactured by Cybex Corporation located in Huntsville, Alabama, analog VGA video levels routed thereby may be reduced and high frequency components of the signal attenuated by switching circuitry inside the COMMANDER module. However, signal degradation may occur due to signal interaction in the cable between the COMMANDER module and the monitor.
In another instance, where analog video and other data signals are coupled to or between workstations via relatively long conductors, similar signal losses occur. In order to compensate for these signal losses, it is generally necessary to regenerate voltage amplitude of the video and data signals prior to inputting them to a monitor and other peripheral devices. Typically such regeneration is done by a pair of transistors coupled in a common emitter configuration, with the first transistor inverting the signal and the second transistor reinverting the signal in order to provide noninverted voltage amplification. While this type of amplifier requires power of a single polarity and ground, DC coupling of the amplifiers is generally difficult to implement and not particularly stable. In any case, some type of amplifier circuitry is required at the monitor end of the cable to regenerate the video signals.
There are also instances where it is desirable to distribute a video signal from a single video source to a plurality of monitors remotely located from the source. One example of these situations include airport terminals, where a single video source, such as a computer, provides scheduling information related to incoming/outgoing flights to monitors located at ticket sales desks or other locations where it is desirable to display such information.
While there are a number of extended video communications links presently available, several of which manufactured by CYBEX corporation, and as far as Applicants are aware, none utilize inexpensive, unshielded twisted pair conductors bundled in a cable to transmit analog computer video signals and separate sync signals.
Accordingly, it is an object of this invention to provide an extended analog video communications link having an unpowered passive receiver network and which may be used to distribute such a video signal from a single source to a plurality of monitors.